Various embodiments may include a method for operating an internal combustion engine comprising: measuring pressure oscillations assignable to a cylinder in the inlet tract at a defined operating point during normal operation; generating a corresponding pressure signal; determining a corresponding crankshaft phase angle; calculating an injection signal component caused by fuel injection by subtracting a reference base pressure oscillation signal; determining a signal phase position and a signal amplitude of the injection signal component; determining an injection start time; determining an injection quantity on the basis of the signal amplitude and reference amplitudes; and adapting operation of the internal combustion engine based on the determined injection quantity.